1. Field of the Invention
The present invention relates to an image forming apparatus which forms an image on a recording material by using an electrophotography technique, such as an electrostatic copier or a printer or the like.
2. Related Background Art
There have recently been widely accepted into markets composite machines each having all kinds of output terminals such as a copier, a printer and a facsimile. Image forming apparatuses which use electrophotographic processes are widely accepted as such output terminals corresponding to networks and there is mentioned as a great problem a limited number of sheets for which a main body continuously operates normally without maintenance, or the so-called duty cycle. One of causes for shortening the duty cycle is a service life of an image bearing body as an image bearing member, and great problems are posed from an ecological viewpoint to reduce consumables, prolong service lives of the consumables and enhance reliabilities.
Furthermore, conventional analog apparatuses are being switched to digital apparatuses and there is posed a theme to equalize or lower a cost of a main body of a digital apparatus relative to a cost of a main body of an analog apparatus. Though conventional copiers and printers are mainly white-black apparatuses, full-color originals and full-color output files are used rapidly in larger amount in offices. A theme is therefore posed to equalize not only equalize the price of the digital apparatus to that of the analog apparatus as described above but also to equalize a cost of a main body and a running cost of a full-color printer to those of a white-black printer. Accordingly, it is desired to develop a technique which permits epoch-making lowering of a total cost ownership (TCO).
Specifically, the duty cycle, the running cost and the like of an image forming apparatus are largely dependent on a service life of the image bearing body, and a cleaning device which removes residual developer from the image bearing body can be mentioned as an electrophotographic process technique for determining the service life of the image bearing body.
It is difficult for a cleaning device of a known image forming apparatus to transfer all developer (hereinafter referred to as a toner) of a developer image formed on a surface of the image bearing body to a transferring material at a transferring time and the toner inevitably remains in some amount on the image bearing body. Furthermore, powder of the transferring material and the like which are produced from the transferring material which is brought into contact with the image bearing body also adhere to the image bearing body. It is therefore necessary to clean the image bearing body sufficiently after each transferring step by removing the toner and the powder of the transferring material remaining on the image bearing body after transferring (hereinafter referred to collectively as transferring residual toner).
Out of various kinds of cleaning means which have conventionally been proposed, a cleaning blade which is made of an elastic material, such as urethane rubber and configured to remove the transferring residual toner by scratching off the residual toner with an edge brought into contact with an image bearing body has already been widely put to practical use as known well since the cleaning blade is simple in a configuration, inexpensive in cost and excellent in function.
The above described cleaning blade has an edge at an end which is kept in contact with a drum like image bearing body in a direction reverse to a driving rotating direction of the above described image bearing body and scrapes off transferring residual toner produced at a location to transfer a toner image to a transferring material when the transferring residual toner attains to a location of the edge of the cleaning blade. However, the cleaning blade utilizes the elastic material of rubber and does not slide since a friction coefficient is remarkably large between the elastic material of rubber and the image bearing body.
When a powder material having a small particle diameter such as a developer used for en electrophotography image forming apparatus is interposed between the elastic material of rubber and the image bearing body, however, the cleaning blade slides on the image bearing body, thereby realizing stable contact of the cleaning blade with the image bearing body which is being driven. Furthermore, a small amount of the transferring residual toner which is scraped off and stagnant is supplied to the cleaning blade as the image bearing body rotates to interpose the powder material, whereby a frictional force is weakened and the cleaning blade can exhibit stable and favorable cleaning performance without being turned over.
In the cleaning device which has the above described configuration, however, not only the friction coefficient but also friction between the cleaning blade and the image bearing body is unstable, and a tip portion of the cleaning blade which is kept in substantial contact with the image bearing body causes a chatter vibration, thereby producing an abnormal noise from the cleaning device or resulting in insufficient cleaning due to lowering of a capability to remove the residue from the surface of the image bearing body.
In order to solve these problems, there have been adopted means for stabilizing a slide condition by mixing a lubricant with a toner and means for selecting a contact condition where the cleaning blade is hardly loaded. For preventing stick-slip which causes a chatter vibration phenomenon in particular, there have been proposed a configuration to enhance a rigidity of the cleaning blade and a configuration to reduce an elasticity loss.
However, there lies an obstacle to a durability of the cleaning blade since it is necessary to improve slide portions of the cleaning blade and the image bearing body which constitute an original cause for the chatter vibration phenomenon in order to configure the cleaning blade so as to be durable of long-term use and the chatter vibration phenomenon cannot be prevented by means for simply weakening a frictional force.
The stick-slip phenomenon which causes the chatter vibration phenomenon of the cleaning blade is caused roughly by a coefficient of static friction which is larger than a coefficient of kinetic friction. When the cleaning blade is shifted from a condition where the cleaning blade adheres (sticks) to the image bearing body with a strong static frictional force to kinetic friction by driving the image bearing body, for example, a coefficient of friction is reduced and the cleaning blade abruptly slips, and thereby is released from distortion. Accordingly, shearing forces of the cleaning blade and the image bearing body which oppose a frictional force, whereby the cleaning blade is again in the condition adhering the image bearing body. When the stick-slip phenomenon is repeated at a high speed, the cleaning blade is vibrated, thereby posing a problem of chattering or emitting of the abnormal noise.
The present invention has been achieved in view of the above described problems and has an object to provide an image forming apparatus which is capable of exhibiting stable cleaning performance irrespective of a moving speed of an image bearing body.
Another object of the present invention is to provide an image forming apparatus including: an image bearing member; and a cleaning blade for cleaning said image bearing member, in which a friction coefficient between the image bearing member and the cleaning blade is denoted by xcexc a decreasing ratio of the friction coefficient xcexc relative to a common logarithm of a moving speed of the image bearing member is 0.03% or lower.
Further objects of the present invention will be apparent upon a reading of the following detailed description in connection with the accompanying drawings.